Water-quality gradients shape functional-trait variation and dominance of invasive macrophyte Pontederia crassipes in tropical wetlands

Environmental gradients mediate the invasion success of aquatic macrophytes and determine strategies of functional-trait expression and allocation. We sampled 15 wetlands across five climatic zones in Assam, northeast India. We tested how water-quality heterogeneity affects trait variation and dominance of Pontederia crassipes. We measured key physicochemical parameters of water and assessed the morphological functional traits of P. crassipes. Climatic zones differed significantly in water environmental conditions, including dissolved oxygen, ionic composition, total alkalinity, and nutrient availability, with consistent spatial patterns within zones. P. crassipes also showed significant functional trait variation across zones, suggesting context-dependent allocation and water-relations strategies. Group-wise PCA revealed distinct multivariate structuring of both water chemistry and plant traits across zones, suggesting that a limited number of trait syndromes underlie performance in heterogeneous habitats. Random Forest models identified non-linear, trait-specific environmental drivers, with variables related to nutrients, ionic composition, depth, and temperature emerging as key predictors depending on the trait. Trait-importance ranking further highlighted allocation ratios and water-relation traits as disproportionately influential compared to absolute biomass traits. Overall, these findings demonstrate that dominance of P. crassipes is associated with environmentally mediated shifts in coordinated trait syndromes rather than a single uniform growth strategy. Trait-based indicators linked to water chemistry can therefore support targeted, zone-specific management of invaded wetlands under increasing nutrient loading and hydroclimatic variability.